1. Field of the Invention
This invention relates to an improvement in an apparatus for measuring ion concentrations such as pH, calcium ion, potassium ion, etc. and, more particularly, to apparatus for providing an efficient calibration of the measuring instrument.
2. Description of Related Art
As examples of a pH meter for measuring the pH of a solution, reference can be made to FIG. 4, wherein a plastic body main part has a measuring portion 42 comprising an ion responding portion of a measuring electrode and a reference electrode liquid junction at the tip end. A plastic protection cap 43 can be removably attached and can hold a calibration liquid which is used for calibrating the pH meter. A ring assembly 44 can be used to protect the measuring portion 42 when the protection cap 43 is removed.
The conventional pH meter disclosed in FIG. 4 has an advantage in that attaching the protection cap 43 to the measuring portion 42 can not only protect the measuring portion 42 during storage, but it can also provide calibration fluid to the measuring portion during the storage nonmeasuring period.
The protection cap 43 is constructed separately from the body 41 of the pH meter and, thus, a disadvantage occurs in operation in the field in that the cap can be easily lost, requiring measures to ensure that the cap is not lost to the detriment of the instrument. When the measuring portion 42 is to be calibrated just prior to a measurement, the removed protection cap 43 must be attached to the top end of the body 41, which sometimes renders the operation troublesome to the field operator.
An example of a pH and specific ion concentration measuring instrument can be seen in U.S. Pat. No. 5,124,659. U.S. Pat. No. 5,511,408 discloses an automatic calibrating apparatus wherein calibration can be accomplished when the sensor member is inserted into a chamber during a storage mode of operation. The art is still seeking to improve ion concentration measuring apparatus.